Round bearing

ABSTRACT

Round bearings comprise (i) an outer bush, (ii) a bearing element based on polyisocyanate polyadducts and (iii) a hollow inner bush. A surface of the outer bush and/or the hollow inner bush that is adjacent to (ii) the bearing element containing thermoplastic polyurethane.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to bearings.

2. Description of the Related Art

Round bearings are used inside the chassis of automobiles and formounting assemblies and are generally known. With the aid of roundbearings, assemblies, chassis components, etc. are connected to oneanother or to the bodywork with the aid of round bearings. Through theuse of elastomer materials, they perform the function of an elasticbearing; on the other hand, owing to their viscous properties, they arecapable of dissipating energy and hence damping vibrations. A highdegree of damping is required in particular for damping large amplitudesof low-frequency vibrations which influence, for example, the connectionof shock absorbers to the bodywork. On the other hand, for reasonsrelating to vehicle acoustics, high damping is undesired in the case oflow amplitudes and higher frequencies. The damping behavior of current,conventional round bearings is dependent on the intrinsic dampingcapacity of the elastomer material used.

SUMMARY OF THE INVENTION

The present invention relates to round bearings comprising (i) apreferably cylindrical outer bush, (ii) a preferably cylindrical,preferably hollow bearing element based on, preferably, cellularpolyisocyanate polyadducts, preferably based on cellular polyurethaneelastomers which, if required, may contain polyurea structures,particularly preferably based on cellular polyurethane elastomerspreferably having a density, according to DIN 53 420, of from 200 to 1100, preferably from 300 to 800, kg/m³, a tensile strength, according toDIN 53571, of ≦2, preferably from 2 to 8, N/mm², an elongation,according to DIN 53571, of ≦300, preferably from 300 to 700, % and atear propagation strength, according to DIN 53515, of ≦8, preferablyfrom 8 to 25, N/mm, which are preferably surrounded by the outer bush,and (iii) a hollow, preferably cylindrical inner bush which ispreferably positioned in the bearing element (ii). The present inventionalso relates to automobiles or trucks comprising the novel roundbearings.

BRIEF DESCRIPTION OF THE DRAWINGS

Novel round bearings are shown in FIGS. 1 to 4.

FIG. 1 shows a round bearing comprising inner bush (iii), bearingelement (ii) and outer bush (i);

FIG. 2 shows a round bearing in which the inner bush consists of anexternal inner bush (vi) containing TPU and an internal inner bush (vii)comprising metal;

FIG. 3 shows a round bearing in which the outer bush consists of aninternal outer bush (iv) containing TPU and an external outer bush (v)comprising metal; and

FIG. 4 shows a round bearing comprising a two-part inner and outer bush.In the figures, the individual bushes are shown projecting for greaterclarity.

According to the invention, the individual bushes/bearing elements mayhave the same height. It is also possible for the inner parts of theround bearing to have a smaller height than the outer parts, whereas inthe figures the inner parts have a greater height and project.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is an object of the present invention to provide round bearingscomprising (i) an outer bush, (ii) a bearing element based on cellularpolyisocyanate polyadducts and (iii) a hollow inner bush, in which theadhesive bond between the bearing element and the hollow inner bush isno longer to be achieved by means of an adhesion promoter. Forapplications where a round bearing had to be joined by means of a screwconnection, the use of a metallic sleeve should be possible, andimproved corrosion protection was required.

We have found that this object is achieved if that surface of (i) and/or(iii) which is adjacent to (ii) the bearing element containsthermoplastic polyurethane with or without glass fiber filler and/orpolyurethane casting elastomers, preferably thermoplastic polyurethane.

By using thermoplastic polyurethane, also referred to below as TPU, itis ensured that it is possible to dispense with the use of chemicaladhesion promoters in the connection of the bearing element, becausecellular polyisocyanate polyadduct forms a very good adhesive bond toTPU. Through the preferred use of the TPU in combination with a metallicinsert, the inner bush can be used for a screw connection. Thecombination of TPU and metal to give a hollow inner bush, in the form ofan interlocking, frictional or integral connection, makes it possible inparticular to dispense with a special corrosion protection of themetallic parts through the use of stainless steel or aluminum. Thus, theabovementioned requirement could be met by this combination of differentmaterials. Alternatively or in addition to the particularly preferredTPUs, generally known polyurethane casting elastomers can be used. Incontrast to the TPUs, the casting elastomers are usually crosslinkedpolyurethanes.

Thermoplastic polyurethanes are generally known and commerciallyavailable, for example from Elastogran GmbH, Germany. Preferably, thethermoplastic polyurethane has a hardness of from 60 Shore A to 85 ShoreD. The TPUs can, if required, also be used in generally known mixtureswith further thermoplastics, for example polyolefins, ABS and/or ASAplastics, and fillers, e.g. glass fibers. The TPUs are preferably notused as a mixture with other plastics but contain glass fibers as afiller. The TPUs may be based on generally known raw materials, forexample the generally customary isocyanates, polyols, chain extenders,catalysts and assistants. The production both with TPU-coated innerand/or outer bushes or with these bushes completely based on TPU ormixtures of TPU with other thermoplastics is generally known andfamiliar to a person skilled in the art. For example, the inner and/orthe outer bush can be produced from the TPU by means of injectionmolding. Coating of prefabricated metal bushes with TPU sheets, whichwere melted on the desired surface of the bush, is also possible. Thethickness of the TPU which is adjacent to the bearing element (ii) ispreferably from 1 to 15 mm.

The inner bush (iii) can, for example, be completely based onthermoplastic polyurethane. Alternatively, it is possible for the innerbush (iii) to comprise an external bush (vi) directed toward the bearingelement (ii) and based on thermoplastic polyurethane and an internalbush (vii) adjacent to the external bush (vi) and based on metal, e.g.steel, iron and/or aluminum. In the two-part version, the bushes (vi)and (vii) are preferably connected to one another by an integral,interlocking or frictional connection, for example by adhesively bondingthem to one another, screwing one into the other or pressing one ontothe other. For example, adhesion between the bushes can be achieved bymelting a TPU sheet as (vi) internal bush onto the external bush. Theinner bush (iii) has an inner bore, usually for receiving a fasteningbolt. The external diameter is determined by the design.

In applications where no adhesive bond is required between that surfaceof the inner bush which faces the bearing element, said inner bush canbe provided with a, preferably, attached collar which runs all round,preferably perpendicular to, the inner bore and preferably on the outersurface of the inner bush (iii). Said collar may vary in diameter,thickness, design and number. The collar forms the preferred frictionalsurface in the case of a radial load on the side walls anddisplacement-limiting means on compression of the suspension in the caseof a load on the end face. This contour also has particularlyadvantageous characteristics when cardanic loads occur. Preferably, thebearing element (ii) does not project beyond the inner bush in the axialdirection.

According to the invention, the bearing element (ii) may consist of oneor more individual parts which have elastic properties. If at least twobearing elements are used, they may be joined, so to speak, in aconnected system to give the complete bearing element, it being possibleto choose generally known connecting methods, for exampletongue-and-groove. It is therefore possible to produce bearing elementswhich have different properties and, depending on their arrangement inthe round bearing, can meet specific requirements. If at least twobearing element (ii) are used, they preferably have different densitiesand hence different mechanical and dynamic properties. While, forexample, a bearing element (ii) may consist of a microcellular PU havinga low density, in order to generate a great deal of damping by therelative movement of inner and outer bush during use, the furtherbearing element (ii) in the round bearing may be produced from amicrocellular PU having a high density, in order to ensure dynamicrigidities and to reduce the maximum deformation. According to theinvention, it is therefore possible to meet specific requirements.Bearing elements (ii) comprising preferably compact TPU are alsoconceivable. The novel bearing element (ii) is preferably based onelastomers based on polyisocyanate polyadducts, for examplepolyurethanes and/or polyureas, for example polyurethane elastomerswhich, if required, may contain urea structures. The elastomers arepreferably microcellular elastomers based on polyisocyanate polyadducts,preferably with cells having a diameter of from 0.01 to 0.5 mm,particularly preferably from 0.01 to 0.15 mm. Particularly preferably,the elastomers have the physical properties described at the outset.Elastomers based on polyisocyanate polyadducts and their preparation aregenerally known and widely described, for example in EP-A 62 835, EP-A36 994, EP-A 250 969, DE-A 195 48 770 and DE-A 195 48 771. Thepreparation is usually carried out by reacting isocyanates withcompounds reactive toward isocyanates. The elastomers based on cellularpolyisocyanate polyadducts are usually prepared in a mold, in which thereactive starting components are reacted with one another. Suitablemolds here are generally customary molds, for example metal molds which,owing to their shape, ensure the novel three-dimensional shape of thespring element. The preparation of the polyisocyanate polyadducts can becarried out by generally known processes, for example by using thefollowing starting materials in a one- or two-stage process:

(a) isocyanate,

(b) compounds reactive toward isocyanates,

(c) water and, if required,

(d) catalysts,

(e) blowing agents and/or

(f) assistants and/or additives, for example polysiloxanes and/or fattyacid sulfonates.

The cellular polyisocyanate polyadducts preferably have a compressionset of less than 25% according to DIN 53572, the test specimens usedbeing blocks measuring 40 mm×40 mm×30 mm without a silicone coating, thetest is carried out at constant deformation, the test specimens beingcompressed by 40% and kept for 22 hours at 80° C. in athrough-circulation oven, the test apparatus is cooled to roomtemperature for 2 hours in the compressed state after removal from theoven and then the test specimen is removed from the test apparatus and,10 min±30 s after the removal of the test specimens from the testapparatus, the height of the test specimens is measured accurately to0.1 mm. The bearing element (ii) is preferably adhesively bonded to thethermoplastic polyurethane of the outer bush (i) and/or of the innerbush (iii). The expression adhesively bonded is to be understood asmeaning in particular that the bearing element (ii) is stuck to the TPU,for example using generally customary adhesives, or is foamed directlyon the TPU. A preferably used adhesive is a reactive hotmelt adhesive,preferably based on encapsulated isocyanates, having a melting range attemperatures of less than 95° C., preferably from 30 to 90° C.,particularly preferably from 45 to 65° C., and a reaction range attemperatures preferably greater than 100° C., particularly preferablyfrom 110 to 125° C. Such reactive hotmelt adhesives are available fromCollano Ebnother AG, Sempach-Station, Switzerland, and are described inthe article Vorapplizierbare PUR-Hotmelts: Aktivierung per Wärmestoβ,Adhasion Kleben und Dichten, 43rd year, 10/99, pages 22 to 24. Theproduction of the bearing element on the surface of the TPU can beeffected by generally known methods, for example by placing thecorresponding TPU sleeve in a mold and preparing the cellularpolyisocyanate polyadduct in this mold.

The outer bush (i) may be based completely on thermoplasticpolyurethane. Alternatively, it is possible for the outer bush (i) tocomprise an internal bush (iv) directed toward the bearing element (ii)and based on thermoplastic polyurethane and an external bush (v)adjacent to the internal bush (iv) and based on metal, e.g. steel, ironand/or aluminum. In the case of the two-part version, the bushes (iv)and (v) are preferably adhesively bonded to one another, for example bysticking them to one another. For example, adhesion between the bushescan be achieved by melting a TPU sheet as (iv) internal bush onto theexternal bush. The outer bush (i) has an external diameter and aninternal diameter which can vary in dimensions and form. The presentinvention relates to both sized and unsized bushes. Fixing of theindividual parts, i.e. inner bush (iii), bearing element(s) (ii) andouter bush (i) can be achieved, for example, by sizing. For example,during assembly, the individual parts can be joined together in theouter bush, the external diameter of the inner bush being slightlysmaller than the internal diameter of the outer bush. After all partshave been joined together, the outer bush can then be made smaller indiameter, with the result that the inserted parts are fixed to oneanother. The outer bush may also be designed in such a way that it iscompleted with the elastomer materials and the inner bush before aone-part or multipart shaping process for final shaping. The elastomerparts may have a larger external diameter than the internal diameter ofthe outer bush. An initial stress of the elastomer component is thusachieved. In the case of this method of construction, it is possible todispense with a subsequent sizing process. These advantages also applyif the internal diameter of the elastomer components is smaller than theexternal diameter of the inner bush.

Preferably, the bearing elements (ii) are positioned with an exact fitin the outer bush (i) and the inner bush (iii) with an exact fit in thebearing element, which may be composed of the individual bearingelements (ii), so that the parts are fixed to one another in such a waythat the total bearing element consisting of the individual bearingelements (ii) rubs both against (i) and against (iii) if this is desiredby the design.

1. A round bearing for use inside a chassis of automobiles and formounting assemblies, comprising: an outer bush; a bearing element basedon cellular polyisocyanate polyadducts; and a hollow inner bush, whereina surface of the outer bush and/or the hollow inner bush, which isadjacent to the bearing element based on cellular polyisocyanatepolyadducts, is formed of thermoplastic polyurethane and/or polyurethanecasting elastomers.
 2. A round bearing as claimed in claim 1, whereinthe outer bush includes an internal bush directed toward the bearingelement and based on thermoplastic polyurethane and an external bushadjacent to the internal bush and based on metal.
 3. A round bearing asclaimed in claim 1, wherein the hollow inner bush is based onthermoplastic polyurethane.
 4. A round bearing as claimed in claim 1,wherein the hollow inner bush includes an exterior bush directed towardthe bearing element and based on thermoplastic polyurethane and an innerbush adjacent to the exterior bush and based on metal.
 5. A roundbearing as claimed in claim 2, wherein the internal bush and externalbush are adhesively bonded.
 6. A round bearing as claimed in claim 4,wherein the exterior bush and inner bush are adhesively bonded.
 7. Around bearing as claimed in claim 1, wherein the thermoplasticpolyurethane adjacent to the bearing element has a thickness of from 1to 15 mm.
 8. A round bearing as claimed in claim 1, wherein the bearingelement is adhesively bonded to the thermoplastic polyurethane of atleast one of the outer bush and the hollow inner bush.
 9. A roundbearing as claimed in claim 1, wherein the thermoplastic polyurethanehas a hardness of from Shore 60 A to Shore 85 D.
 10. An automobilecomprising a round bearing as claimed in claim
 1. 11. A round bearing asclaimed in claim 1, wherein the thermoplastic polyurethane contains aglass fiber filler.